1. Field of the Invention
The invention relates to an electron-beam vaporization installation for coating structural components made of extreme-heat-resistant alloy (super alloys), especially turbine blades, with thermal barrier coatings (TBC). The protective coatings permit higher operating temperatures for thermal engines result in a higher thermal efficiency. The design of the installation permits a productive coating of the substrata by a continuous process.
2. Description of Related Art, Including Information Disclosed Under 37 CFR 1.97-1.99.
Known prior installations for coating TBC use a batch operation process and consist primarily of charging chamber, heating chamber, vaporization chamber with linearly arranged vaporizer crucibles, transport installation for the substrata, electron gun, associated evacuation equipment and the necessary peripheral components. To obtain the necessary adhesive strength of the layers the structural components are preheated to temperatures above 1000.degree. C. Furthermore, during the vaporization the structural components have to be moved over the vapor source in order to obtain an as uniform as possible thickness of the layer. Because of the high process temperatures the chambers are water cooled and can be separated by valves also water cooled. Therefore, a ventilation of the heating and the vaporization chambers is not required. While the valve between the charging chamber and the heating chamber is absolutely necessary, the valve between the heating chamber and the vaporization chamber is only needed, when the vaporization chamber has to be opened for maintenance or for an exchange of the vaporizing material, or when during a reactivating coating the entrance of oxygen into the heating chamber is temporarily to be limited.
A carriage with a changing pole of a corresponding length is used for the transport of the substrata through the chambers. The charging pole has at the equipment end the mechanics for a substratum holder, making possible also the turning and swiveling of the substratum and the eventual installation of cooling water and sensor conduits. By using exchangeable substratum holders the simultaneous coating of several smaller substrata is made possible. Normally the other end of the charging pole is installed rotatably in a carriage. The long charging pole, above to withstand thermal stress or water cooled, permits the transport of the substrata inside or through the hot zones, without the carriage with its drive is being exposed to the extremely high temperatures.
In smaller installations this carriage is mostly located in the atmosphere and the water cooled charging pole reaches through a rotary and sliding transit into the installation. While this allows a shorter charging chamber and a smaller volume of the installation, the cost, however, the cost for the calibrated pole and the sliding rotary transit is high.
On the other hand in large installations the carriage runs mostly in the charging chamber which can be evacuated. This has the advantage that there are no special requirements for the surface condition of the charging pole. Instead of the expensive rotary and sliding transits, only rotary transit for inside spindles are needed. These transport the carriage and transfer to it the rotation and swivel movements. With this solution the horizontal drive does not have to absorb the large forces due to air pressure, on the charging pole. The disadvantages, of both of these embodiments with charging pole, are their lack of flexibility. If in the course of technological development it becomes necessary to install additional processing chambers or work stations then the charging pole would have to be lengthened accordingly. There are, however, limits to such a lengthening due to the diminishing stiffness for a given cross-section. In addition, each lengthening of the chamber entails the double lengthening of the installation. But even without this aspect the prior known designs have disadvantages because of the high construction costs, their great length, and the corresponding large space requirement of the installation and therewith large costs.
There is also the possibility to mount the substratum receiver directly at the transport carriage without using a charging pole. The transport carriage is then moved inside the chambers by a cooled roller system. This solution has the disadvantage that for the thermal shielding of the carriage an additional intermediate chamber has to be installed, between the heating chamber and the coating chamber, in which the transport carriage is located during the coating.
The common disadvantages of the described designs are that because of the charge process in which work pieces are treated together within the heating chamber. The work pieces are positioned on a carrier until it is filled. Then the carrier is placed in a preheating chamber where work pieces are heated together to the given temperature. Then the carrier is transported to the vaporization chamber operation. The time for a vaporizing cycle consists of the sum of the process times at the individual stations of the installation. For a partial solution of this problem the chambers for performing the auxiliary processes "vacuum passing lock" and "preheating" were arranged mirror-inverted on both sides of the vaporizing chamber and two or four mechanisms are used for the substrata transport. Such installations are equipped, for instance, with four movable charging chambers and four heating chambers. This solution, therefore, is very expensive in space and costs.
Using an installation working according to the continuous processing principle would solve the problems mentioned. The prior known transport systems, however, cannot be employed for the solution of the coating problem at hand because of the extreme high thermal stresses in the heating the coating chambers.